Hydraulic Fracturing Composition

ABSTRACT

The invention relates to subterranean treatment fluids, and more particularly for hydraulic fracturing formulations, comprising a low viscosity hydrocarbon fluid having low pour point and low or no BTEX content combined with suitable additives, in particular with a thickening agent additive.

PRIORITY CLAIM TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.Nos. 61/731,116 filed Nov. 29, 2012 and 61/731,318 filed Nov. 29, 2012,the disclosures of which are fully incorporated herein by theirreference.

FIELD OF THE INVENTION

The invention relates to a composition comprising a low viscosityhydrocarbon fluid having low or no benzene, toluene, ethylbenzene, orxylene (BTEX) compounds and the viscosification of the same for use insubterranean treatment fluids, especially for use in hydraulicfracturing formulations.

BACKGROUND OF THE INVENTION

In the recovery of petroleum and natural gas from subterraneanreservoirs several different liquids are generally used having differentfunctional designations. Examples of such designations are: drillingfluid (drilling mud), cement slurry, completion fluid, packer fluid,perforation fluid, gravel packing fluid, acidizing fluid and fracturingfluid.

Hydraulic fracturing is an example of technologies that contribute toimprovements in oil and gas production. Hydraulic fracturing is used tocreate additional passageways in the oil, gas, and/or coalbed reservoirthat can, by way of example, facilitate the flow of oil and/or gas to aproducing well. Unconventional reservoirs such as shale gas reservoirs,coalbed methane reservoirs, and “tight gas” reservoirs, such as thosewhose gas-containing matrix have restricted porosity and permeabilitythat impede the flow of oil or gas through the reservoir, are commonlyfractured by injecting a fluid containing sand or other “proppant” andother ingredients under sufficient pressure to create fractures in therock through which the desired product can more easily flow.

Diesel is an example of an ingredient that has been used in hydraulicfracturing formulations and/or in additives that are used in hydraulicfracturing formulations. Diesel is considered by many in the industry tohave sufficiently high viscosity to suspend solid additives in slurrytype formulations, but contains constituents regulated under the SafeDrinking Water Act (SDWA) because of their potential toxicity, includingbenzene, toluene, ethylbenzene, and xylenes (BTEX chemicals).

Various alternative fluids have been proposed to address these concernsand numerous compositions proposed for hydraulic fracturing.Representative examples include GB 2.084.632; WO 1989-001491; WO2000-022063; U.S. Pat. No. 6,017,854; and U.S. Patent ApplicationPublication 2008/0318812. U.S. Patent Application Publication2008/0318812, in particular, specifies a hydrocarbon fluid having aviscosity of at least 5 centistokes (5 cSt or 5×10⁻⁶ m²/s).

It has been noted (EPA web site information, as adapted from Powell etal., 1999) that hydraulic fracturing fluids should have the followingcharacteristics: (i) be viscous enough to create a fracture of adequatewidth; (ii) maximize fluid travel distance to extend fracture length;(iii) be able to transport large amounts of proppant into the fracture;(iv) require minimal gelling agent to allow for easier degradation or“breaking”; and (v) reduced cost.

Some fluids which would otherwise be suitable for use in hydraulicfracturing applications may not be effectively formulated due to havingrelatively low viscosity, causing phase separation or settling ofsuspended formulation constituents. Accordingly, there is a need forformulations that avoid phase separation and settling and that are morestorage-stable.

Moreover, there is also the problem that formulations transported fromthe formulation site to the field may undergo extreme temperaturevariations which alter the physical properties of the formulations,e.g., settling of suspensions when fluid viscosity decreases further dueto increasing temperature. On the other hand, an extreme decrease intemperature may result in a formulation which becomes unpourable, due tothe fluid having a pour point which is too high. Accordingly, there is aneed for formulations that are more robust with respect to change intemperature.

Accordingly, it would be highly beneficial if alternative fluids orremedies could be found that could address all of the shortcomings ofthe prior art.

The present invention relates, in embodiments, to the use of a lowviscosity hydrocarbon with a thickening agent and low pour point havinglow or no BTEX compounds in hydraulic fracturing formulations andhydraulic fracturing processes.

SUMMARY OF THE INVENTION

The invention is directed to use of a hydrocarbon fluid having akinematic viscosity of about 2.20 cSt (25° C.) or less (ASTM D445), apour point of −35° C. or less (ASTM D97), a total aromaticsconcentration of 0.02 wt % maximum (AM-S 140.31), and preferably apolycyclic aromatic hydrocarbon (PAH) content of less than 10 mg/kg, andpreferably further characterized as having “not detected” (ND) levels,by GC/Mass Spectrometry, of benzene, toluene, ethylbenzene, and xylenes(BTEX; practical quantitation limits are benzene=0.2 mg/kg, toluene=0.3mg/kg, ethylbenzene=0.1 mg/kg, o-xylene=0.1 mg/kg, m-xylene plusp-xylene=0.1 mg/kg), in a hydraulic fracturing process, and to acomposition for hydraulic fracturing comprising said hydrocarbon fluidand at least one, preferably both, of: (i) a suspension agent, such asguar, derivatized guar, and the like, and (ii) a thickening agent,preferably characterized as suitable to provide a composition with aviscosity of 2.70 cSt or higher, preferably about 3-4 cSt or higher, at25° C. (ASTM D445), in combination solely with said hydrocarbon fluid.

In embodiments said composition comprising the hydrocarbon fluid, thesuspension agent, and the thickening agent is characterized asmaintaining a suspension of a polymeric suspension agent such as guarwhen said composition is heated or cooled, such as from ambientconditions to conditions of transport or of use of the final composition(which may be below 0° C.), such as from 70° C. to −30° C., and thelike.

The invention is also directed to a process for recovery of oil and/ornatural gas from subterranean reservoirs using hydraulic fracturingtechniques and hydraulic fracturing fluid composition, the improvementcomprising use of a hydraulic fracturing fluid formulation comprising ahydrocarbon fluid having a kinematic viscosity of about 2.20 cSt (25°C.) or less, a pour point of −35° C. or less, a total aromaticsconcentration of 0.02 wt % maximum, and preferably a polycyclic aromatichydrocarbon (PAH) content of less than 10 mg/kg, and preferably furthercharacterized as having “not detected” (ND) levels of benzene, toluene,ethylbenzene, and xylenes (BTEX), and at least one and preferably bothof: (i) a suspension agent, such as guar, derivatized guar, and thelike, and (ii) a thickening agent characterized as suitable to provide aformulation with a viscosity of 2.7 cSt or higher, preferably about 3-4cSt or higher at 25° C. in combination solely with said hydrocarbonfluid. It is an object of the invention to provide a formulation thatuses, as a base fluid, a hydrocarbon fluid heretofore believedunsuitable for hydraulic fracturing formulations because of its lowviscosity, but otherwise having advantageous characteristics including,in embodiments, one or more of low or no BTEX content, availability,relative ease and safety of usage.

It is still further an object of the invention to provide a pre-mixedformulation comprising the aforementioned low viscosity, low pour pointhydrocarbon fluid, and one or more thickening agents, that inembodiments is storage stable, and can be provided to an intermediate orend user to be further modified for final use in the field for oil andgas production.

These and other objects, features, and advantages will become apparentas reference is made to the following detailed description, preferredembodiments, examples, and appended claims.

DETAILED DESCRIPTION

According to the invention, hydrocarbon fluids having a kinematicviscosity of about 2.20 cSt (25° C.) or less, a pour point of −35° C. orless, a total aromatics concentration of 0.02 wt % maximum, andpreferably a polycyclic aromatic hydrocarbon (PAH) content of less than10 mg/kg, and preferably further characterized as having “not detected”(ND) levels of benzene, toluene, ethylbenzene, and xylenes (BTEX), areused in hydraulic fracturing formulations (including intermediate andfinal end-use formulations), and processes using the same. Heretoforesuch fluids were considered to lack the proper viscosity for use incertain hydraulic fracturing formulations. However surprisingly it hasbeen found that with appropriate viscosification, slurries of guar, guarderivatives, and the like, can be prepared from said fluids whichprovide significant advantages over what is suggested in the prior art,particularly with respect to low or no BTEX content, and which, inembodiments are stable, that is, no visible phase separation of saidhydrocarbon fluid and viscosifier, even at low or high temperatures. Inpreferred embodiments, there is also no phase separation of thesuspension agent, e.g., guar, from the hydrocarbon fluid andviscosifier. However, in other embodiments, up to 5 wt %, such as up to2 wt % of separation of the suspension agent is acceptable.

The hydrocarbon fluids useful herein are normal paraffinic,isoparaffinic, cycloparaffinic, and dearomatized mixed aliphatic(normal, branched, and cyclic paraffins) fluids, and mixtures thereof.The most preferred dearomatized mixed aliphatic fluids are dearomatizedmixed aliphatic solvents containing linear, branched, and cyclicparaffins which have aromatics removed or significantly reduced (e.g.,<0.02 wt %). In preferred embodiments such hydrocarbon fluids are alsocharacterizable as having no or low BTEX content.

Particularly preferred fluids are Escaid™ Fluids, commercially availablefrom ExxonMobil Chemical Company, Baytown, Tex., USA, most particularlyEscaid™ PathFrac™ Fluid, a mixture of de-aromatized aliphatic moleculescomposed of normal, branched, and cyclic alkanes, and having a kinematicviscosity of about 2.20 cSt (25° C.), a pour point of −35° C. or less, atotal aromatics concentration of 0.02 wt % maximum, a polycyclicaromatic hydrocarbon (PAH) content of less than 10 mg/kg, and having“not detected” (ND) levels of benzene, toluene, ethylbenzene, andxylenes (BTEX).

Particularly useful thickening agents include such known andcommercially available polymeric viscosifying agents available fromKraton, for example Kraton™ G1701 polymer or Kraton™ G1650 polymer.

Particularly useful thickening agents also include such known andcommercially available polyalphaolefins (PAOs) available from ExxonMobilChemical Company, Baytown, Tex., particularly SpectraSyn™ grade PAOs,more particularly SpectraSyn™ Elite™ 65 PAO, SpectraSyn™ Elite™ 150 PAO,both of which are metallocene PAOs (mPAOs, produced with metallocenecatalysts), and SpectraSyn™ 100 PAO. As used herein, the term “PAO”includes mPAO.

The thickening agent is dissolved in the hydrocarbon fluid typicallywith the use of heat and agitation as necessary. The viscosity of thehomogenous solution is then measured, for example, using test methodASTM D7042 and a viscometer instrument such as an Anton Paar™ SVM 3000.In preferred embodiments a polymeric viscosifying agent is used as thethickening agent in the amount of from 0.3 to 1.0 wt %, preferably 0.4to 0.7 wt %, based on the amount of hydrocarbon fluid (without solidmaterial to be suspended, e.g., guar). In other preferred embodiments aPAO viscosifying agent is used as the thickening agent in the amount offrom 5.0 to 20.0 wt %, based on the amount of hydrocarbon fluid (withoutsolid material to be suspended, e.g., guar). For instance, using 10 wt %SpectraSyn™ Elite™ 65 PAO in Escaid™ Pathfrac™ Fluid provides a solutionhaving a viscosity of about 3.24 cSt at 25° C., and 10 wt % SpectraSyn™Elite™ 150 PAO in Escaid™ Pathfrac™ Fluid provides a solution having aviscosity of about 3.77 cSt at 25° C.

In addition to guar and derivatives thereof, xanthan and derivativesthereof, hydroxy-ethyl cellulose, carboxymethylhydroxyethyl cellulose,and derivatives of such cellulosic materials, or other polysaccharidepolymers known to be useful in hydraulic fracturing compositions aspolymeric suspension agents, and mixtures thereof, are also usefulherein. Accordingly, such additives are broadly referred to herein as“suspension agent”. In embodiments and among other characteristics, thesuspension agent is provided in order to assist in the suspension and/ordelivery of the proppant (discussed below). In embodiments, one or moresuspension agents are added in an amount sufficient to suspend theparticulate material, i.e., proppant (discussed below) and reducesettling during storage, transportation, and use in the fracturingprocess. Also useful in this regard are friction reducing agents such aspolyacrylamide inverse emulsions.

The term “proppant” as used herein, takes the meaning well known in theart. The term “proppant” refers to a granular substance suspended in thefracturing fluid during the fracturing operation. Proppants usefulherein are familiar to those skilled in the art, such as sand,resin-coated sand, sintered bauxite, glass beads, and the like, andincludes mixtures thereof.

The final hydraulic fracturing formulation may contain a variety ofadditional materials, in addition to those mentioned previously, whichmay be included in the fracturing fluid formulation or added at thesite, to perform desired task, such as friction reduction, formationclean up, foam stabilization, leakoff inhibition, surface tensionreduction, or carrying or dissolving other ingredients. These additivesinclude friction reducers, liquid gelling agents, biocides, fluid-lossagents, enzyme breakers, acid breakers, oxidizing breakers, andsurfactants such as emulsifiers and non-emulsifiers. Several productsmay exist in each of these categories.

The composition of the present invention, in combination with otherappropriate additives known in the art may also be used in drilling,completion, work-over and stimulation of wells drilled for petroleumsources.

While the illustrative embodiments of the invention have been describedwith particularity, it will be understood that various othermodifications will be apparent to and can be readily made by thoseskilled in the art without departing from the spirit and scope of theinvention.

Trade names used herein are indicated by a ™ symbol or ® symbol,indicating that the names may be protected by certain trademark rights,e.g., they may be registered trademarks in various jurisdictions. Allpatents and patent applications, test procedures (such as ASTM methods,UL methods, and the like), and other documents cited herein are fullyincorporated by reference to the extent such disclosure is notinconsistent with this invention and for all jurisdictions in which suchincorporation is permitted. When numerical lower limits and numericalupper limits are listed herein, ranges from any lower limit to any upperlimit are contemplated.

What is claimed is:
 1. In a process for recovery of oil and/or naturalgas from subterranean reservoirs using hydraulic fracturing techniquesand hydraulic fracturing fluid composition, the improvement comprisinguse of a hydraulic fracturing fluid formulation comprising a hydrocarbonfluid having a kinematic viscosity of about 2.20 cSt (25° C.) or less(ASTM D445), a pour point of −35° C. or less (ASTM D97), a totalaromatics concentration of 0.02 wt % maximum (AM-S 140.31), and at leastone of: (i) a suspension agent, and (ii) a thickening agent.
 2. Theprocess of claim 1, wherein said hydraulic fracturing fluid formulationis further characterized by at least one of: (i) a polycyclic aromatichydrocarbon (PAH) content of less than 10 mg/kg; and (ii) “not detected”(ND) levels of benzene, toluene, ethylbenzene, and xylenes (BTEX) byGC/Mass Spectrometry.
 3. The process of claim 1, wherein said thickeningagent is characterized as a polymeric viscosity modifier and is presentin the amount of from 0.3 to 1.0 wt %, based on the weight ofhydrocarbon fluid.
 4. The process of claim 1, wherein said thickeningagent is characterized as a PAO and is present in the amount of from 5.0to 20.0 wt %, based on the weight of hydrocarbon fluid.
 5. The processof claim 1, said formulation comprising a thickening agent in an amountsuitable to provide said formulation with a viscosity of 2.70 cSt orhigher, at 25° C. (ASTM D445).
 6. The process of claim 5, wherein saidformulation has a viscosity of about 3-4 cSt or higher, at 25° C. (ASTMD445), when in combination solely with said hydrocarbon fluid.
 7. Theprocess of claim 1, wherein said hydraulic fracturing fluid formulationis characterized as maintaining a stable solution, with respect to theviscosifying agent, when said formulation is exposed to temperatures offrom 70° C. to −30° C.
 8. The process of claim 1, further comprising astep of combining proppant and a composition comprising said hydraulicfracturing fluid formulation.
 9. A formulation comprising a hydrocarbonfluid having a kinematic viscosity of about 2.20 cSt (25° C.) or less(ASTM D445), a pour point of −35° C. or less (ASTM D97), a totalaromatics concentration of 0.02 wt % maximum (AM-S 140.31), and at leastone and preferably both, of: (i) a suspension agent, and (ii) athickening agent.
 10. The formulation of claim 9, further characterizedas having at least one of: (i) a polycyclic aromatic hydrocarbon (PAH)content of less than 10 mg/kg; and (ii) “not detected” (ND) levels ofbenzene, toluene, ethylbenzene, and xylenes (BTEX) by GC/MassSpectrometry.
 11. The formulation of claim 10, comprising a thickeningagent characterized as a polymeric viscosity modifier, present in theamount of from 0.3 to 1.0 wt %, based on the amount of hydrocarbonfluid.
 12. The formulation of claim 11, wherein said polymeric viscositymodifier is present in the amount of from 0.4 to 0.7 wt %, based on theamount of hydrocarbon fluid.
 13. The formulation of claim 10, comprisinga thickening agent characterized as a PAO, present in the amount of from5.0 to 20.0 wt %, based on the weight of hydrocarbon fluid.
 14. Theformulation of claim 9, said formulation comprising a thickening agentin an amount suitable to provide a formulation having a viscosity of2.70 cSt or higher, preferably about 3-4 cSt or higher, at 25° C. (ASTMD445), when in combination solely with said hydrocarbon fluid.
 15. Theformulation of claim 9, characterized as maintaining a stable solution,with respect to the viscosifying agent, when said formulation is exposedto temperatures from 70° C. to −30° C.
 16. The formulation of claim 9,further comprising a suspension agent comprising guar or derivativethereof, and/or a polyacrylamide friction reducer.
 17. The formulationof any one of claims 16, comprising at least one proppant.